BMW i8 gets eye-popping power, fuel economy

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Leading BMW's bold alternative-drive charge is the striking i8, an advanced all-wheel-drive plug-in hybrid revealed here prior to its public debut at the Frankfurt motor show in September.

Initially previewed by the Vision EfficientDynamics concept in 2009, the futuristically styled 2+2 coupe has undergone two years of intensive development and is planned to sit atop the German carmaker's “i” lineup, offering straight-line performance to match that of the M3, combined cycle economy to make even the most frugal Mini model appear thirsty, and a driving experience that BMW insiders describe to AutoWeek as “like nothing else.”

Differing from the pure electric-powered i3, the i8 is planned to go on sale in 2013. It will get a freshly developed gasoline-electric hybrid drive system that allows it to run on electricity or a combination of both traditional combustion and electric power, depending on the driving conditions and the state of battery charge.

Unlike the earlier Vision EfficientDynamics concept--which used a 1.5-liter, three-cylinder common-rail diesel as its prime means of propulsion--the latest incarnation of BMW's hybrid coupe receives a 1.5-liter, three-cylinder direct-injection gasoline engine--essentially the same unit earmarked to head into the next-generation Mini and the front-wheel-drive BMW 1-series due out in 2014.

With 220 hp and 221 lb-ft of torque, the gasoline unit operates in combination with an in-house-developed electric motor rated at 129 hp and 184 lb-ft of torque, for an overall output of 349 hp and 405 lb-ft of torque. The same layout is also earmarked for a third “i” model, the i5, tentatively due out in 2016.

As with the Vision EfficientDynamics concept, the gasoline engine is mounted in back and drives the rear wheels via a dual-clutch gearbox, while the electric motor is set up front and acts on the front wheels through a twin-speed transmission.

When accelerating from a standstill at low speeds and/or with sufficient battery charge, the i8 is capable of running exclusively on electric power in front-wheel-drive mode for distances up to 20 miles. At higher speeds and/or when the battery charge is depleted, the gasoline engine kicks in to provide added performance in all-wheel-drive mode.

BMW says the combined efforts of the gasoline engine and the electric motor give the i8 a 0-to-62-mph time of 4.6 seconds--making it a remarkable 0.3 second faster up the strip than the M3 coupe. The coupe is also claimed to have a 50-to-75-mph time of 4.0 seconds and to reach a top speed limited to 155 mph.

The key to the i8's impressive performance is its comparatively low weight. Boasting body panels fashioned predominately from carbon-fiber-reinforced plastic, the car is claimed to weigh 3,263 pounds. In combination with ultra-low aerodynamic and mechanical drag, the lightweight construction also provides the basis for outstanding fuel economy. BMW puts the i8's combined cycle consumption at 86.6 mpg (U.S.). However, the company claims that the new coupe is capable of bettering this figure in optimal running conditions, suggesting that the definitive production car might be even more economical.

Owing to its hybrid drive, the i8 requires a smaller battery than the pure-electric i3. The liquid-cooled lithium-ion unit is strategically mounted within a floor tunnel running through the center of the cabin. According to BMW, it can be recharged in 1 hour, 45 minutes on a standard 220-volt socket.

BMW also engineered the i8 with a multistage brake-energy-recuperation system that allows the driver to alter the level of charge to the battery under periods of trailing throttle and/or braking. Other fuel-saving features such as automatic stop/start and on-demand operation of functions such as the electric steering, water pump and air conditioning will all be standard.

No figures for overall range have been revealed, but insiders hint that the i8 will be capable of traveling at least 400 miles.

Underpinning the i8 is an aluminum-intensive chassis that uses a double-wishbone front and multilink rear suspension. With much of the car's more weighty mechanical hardware mounted low in the front and rear, BMW is claiming a 50-50 weight distribution and says the i8's center of gravity is lower than that of any existing model.

Stretching to 182.4 inches in length, 77.0 inches in width and 50.4 inches in height, the i8 is slightly longer and wider but a good deal lower than the 3-series coupe.

BMW is also considering launching a convertible version of the i8, complete with a lightweight fabric roof structure.